In recent years, water-absorbent resins are widely used as among components of sanitary materials, such as disposable diapers, sanitary napkins and incontinent pads, for the purpose of causing the water absorbent resins to absorb body liquids.
As to the above water-absorbent resins, the following are known as their examples: partially-neutralized and crosslinked poly(acrylic acids); hydrolyzed graft polymers of starch-acrylonitrile; neutralized graft polymers of starch-acrylic acid; saponified copolymers of vinyl acetate-acrylate esters; crosslinked polymers of carboxymethyl cellulose; hydrolyzed copolymers of acrylonitrile or acrylamide, or crosslinked polymers of these hydrolyzed copolymers; crosslinked polymers of cationic monomers; crosslinked copolymers of isobutylene-maleic acid; and crosslinked copolymers of 2-acrylamido-2-methylpropanesulfonic acid-acrylic acid.
It is said that the above water-absorbent resins are desired to have water absorption properties such as, upon contact with aqueous liquids (e.g. body fluids), high absorption capacity, excellent absorption rate, liquid permeability, gel strength of swollen gel, and suction quantity to suck up water from a base material containing aqueous liquids.
In addition to the above, various attempts are made to provide added functions to the water-absorbent resins by adding thereto deodorizable and antibacterial compounds.
The deodorization is one of performances desirable to absorbent articles, and studies are made to enhance the deodorizability of the water-absorbent resins. Proposed as methods for providing the deodorizability are, for example, methods in which the water-absorbent resins are allowed to contain the follow materials: active carbon (JP-A-105448/1984); extracts from leaves of Theaceae plants (JP-A-158861/1985); essences extracted from coniferous trees (JP-A-241030/1999); manufactured tea (JP-A-041155/1990); tannic acid and complex silicate salt compounds (JP-A-116829/1999).
However, as to the method in which the water-absorbent resins are allowed to contain the active carbon (JP-A-105448/1984), there are problems in that the deodorizing effect is displayed by adsorption of malodorous components to the active carbon, but that the absorbency of the active carbon deteriorates with the passage of time so much that the active carbon becomes deactivated in a period of from the provision to absorbent articles till absorption of urine by the absorbent articles during their practical use. In addition, there are also significant problems in that the active carbon causes black coloring of diapers in the case where used for the diapers.
As to the method in which the water-absorbent resins are allowed to contain the extracts from leaves of Theaceae plants (JP-A-158861/1985), the problems of coloring are improved, but the effect during the practical use is low. In addition, production costs increase because of the extraction from leaves of plants.
As to the method in which the water-absorbent resins are allowed to contain the essences extracted from coniferous trees (JP-A-241030/1999), essential oils such as essences extracted from trees have strong smells peculiar to them and therefore, during the practical use, for example, display a high deodorizing effect of rendering the odor of urine indistinguishable. In such a case, the deodorizing effect is mainly from an odor-masking effect. The deodorization by masking involves the smells peculiar to the essential oils. And there are differences between individuals' tastes for smells, so the essential oils are not suitable as consumer materials aimed at many people. In addition, the essential oils involve production costs.
As to the method in which the water-absorbent resins are allowed to contain the tannic acid and the complex silicate salt compounds (JP-A-116829/1999), the removal effect is displayed upon specific malodorous substances, but the deodorizing effect during the practical use of absorbent articles cannot be said to be enough, probably because there is no effect upon bad smells included in actual body fluids such as urine.
As to the method in which the water-absorbent resins are allowed to contain the manufactured tea (JP-A-041155/1990), the deodorizing effect of the manufactured tea itself is good, but still the deodorizing effect during the practical use of absorbent articles could not be said to be enough, probably because of performances of water-absorbent resins being used.
In addition, by reason of the use for such as absorbent articles, the provision with the deodorizability is always desired to involve high safety.